The present invention relates to metal forming dies and the like, and in particular to a shoulder pilot assembly with self-contained stripper and associated method.
Metal forming dies, such as stamping dies and the like, are well known in the art. Progressive metal forming dies are unique, very sophisticated mechanisms which have multiple stations or progressions that are aligned longitudinally, and are designed to perform a specified operation at each station in a predetermined sequence to create a finished metal part. Progressive stamping dies are capable of forming complex metal parts at very high speeds, so as to minimize manufacturing costs.
Heretofore, the dies used in metal forming processes have typically been individually designed, one of a kind assemblies for a particular part, with each of the various components being handcrafted and custom mounted or fitted in an associated die set, which is in turn positioned in a stamping press. Not only are the punches and the other forming tools in the die set individually designed and constructed, but the other parts of the die set, such as stock lifters, guides, end caps and keepers, cam returns, pilots, etc. are also custom designed, and installed in the die set. Current die making processes require carefully machined, precision holes and recesses in the die set for mounting the individual components, such that the same are quite labor intensive, and require substantial lead time to make, test and set up in a stamping press. Consequently, such metal forming dies are very expensive to design, manufacture, and repair or modify.
Pilot assemblies, such as that disclosed in U.S. Pat. No. 4,342,214, are used for locating a work piece in successive forming stages of a machine, such as a punch press, where the work piece is progressively moved through the forming stages of the machine. The pilot assembly typically includes a pilot pin mounted to a movable die member of the machine for guiding entry into a previously formed hole in a work piece or in a companion die member as the die members are moved toward each other, the pin being axially retractable in its mounting in the event that it strikes an obstruction. The retraction movement of the pin may be controlled by a spring or a hydraulic mechanism which includes a hydraulic chamber formed behind the pin into which the pin moves to displace a hydraulic fluid therefrom.
FIGS. 5-8 illustrate several well known prior art metal forming dies and associated pilot mechanisms, which further represent the background of the present invention. For example, FIG. 5 illustrates one half of a die set 100, which includes a first die member 101 having a plurality of longitudinally spaced apart work stations 102 at which various bending, forming, cut-off and/or punching operations are performed on an elongate strip of metal stock 103. As best illustrated in FIG. 6, the prior art pilot mechanism 104 for the illustrated die set 100 includes a pierce tool punch 105 located at an upstream portion of stock strip 103, which, in the illustrated example, forms a vertically oriented through hole 106 in the stock strip 103 at regularly spaced apart intervals along the stock strip. The through holes or pilot holes 106 are selectively engaged by a series of pilot pins 107 positioned on at least selected ones of the die work stations 102, which serve to precisely locate the stock strip 103 in the work stations, and retain the same in place during the metal forming stroke of the die tools. After each metal forming stroke of the die tools, the pilot pins 107 are retracted out of their associated pilot holes 106 in the stock strip 103, and the stock strip is then shifted longitudinally to the next adjacent work station 102, until the metal part has been completely formed and cut off of the stock strip. When the pilot pins 107 are retracted out of the pilot holes 106 in the stock strip 103, the stock strip tends to stick on one or more of the pilot pins, thereby requiring some type of stripper mechanism to separate them, such that the stock strip can be quickly and sequentially advanced longitudinally through the various die stations.
FIG. 7 illustrates another known prior art pilot assembly that includes a rectangularly shaped block or base 111 that is mounted in a blind hole pocket 112 in an associated upper die member 113. The base block 111 includes a central aperture 114 in which a pilot pin 115 is retained, and two laterally offset reaction apertures 116 in which a pair of stripper assemblies are received and retained. A female punch tool 117 is positioned in the lower die member 122, and closely receives the pilot pin 115 to precisely locate the stock strip 5 in the associated work station 112. Each of the stripper assemblies comprises a plunger shaped rod 118 having an outer end 119 protruding outwardly from base block 111 toward the stock strip 103, and an inner end 120 with a coil spring 121 received thereover which resiliently urges the rods 118 outwardly on opposite sides of pilot pin 15, and serve to strip the stock strip 103 from the exterior surface of the pilot pin 115 as the pilot pin and associated upper die member 113 are raised to a diverged condition relative to the lower die member 122.
FIG. 8 illustrates yet another known prior art pilot assembly, which includes an enlarged, flat mounting plate 126 which attaches to the upper surface 127 of the upper die member 113 using a pair of cap head screws 128 having threaded shanks 129 that are anchored in the upper die member 113. The upper die member 113 includes a central aperture 114 in which a pilot pin 115 is received and retained, along with a pair of reaction apertures 116 disposed on opposite sides of pilot pin 115, each of which receives and retains therein a plunger shaped rod 118. The outer ends 119 of the rods 118 protrude outwardly from the lower surface of upper die member 113, while the inner ends 120 of rods 118 have coil springs 121 received thereon which resiliently urge rods 118 outwardly, such that the outer ends 119 of rods 118 serve to strip the stock strip 5 away from the exterior surface of the pilot pin 115, and thereby permit the stock strip 5 to be shifted longitudinally into the next adjacent work station.
While such prior pilot assemblies have proven generally successful, they are rather expensive and time consuming to construct and install in an associated die set, such that further improvements and enhancements to the same, as well as metal forming dies generally, would be clearly advantageous, and are disclosed herein.